This invention relates to phase comparison radio navigation systems of the kind in which spaced transmitting stations radiate phase-locked signals in a time-shared sequence on one or more different frequencies and in which, at a receiver, the signals from the spaced stations are compared in phase.
If the radiated signals are interrupted or otherwise radiated in such a manner that signals to be compared are not continuously available when required for comparison purposes, it is necessary to provide, in the receiver, phase memories. Such phase memories consist essentially of oscillators which are phase-locked to the appropriate received signals when the latter are available and which serve to make available a continuous output representative of the phases of the intermittently available signals.